Abstract
Individuals with depression experience more negative imagery and less vivid positive imagery, and the late positive potential (LPP) is considered as a viable biomarker for negative attentional and memory biases in depression; however, the LPP response to emotional imagery in depressed individuals remains unclear. This study aims to investigate neural response to emotional imagery in depressed individuals. ERPs were recorded from 40 depressed participants and 44 healthy controls during the encoding-imagery task. Depressed participants scored significantly lower in the valence rating of sad and neutral imagery compared to healthy participants. Importantly, the LPP amplitudes to sad imagery in depressed participants were significantly larger than healthy controls, particularly in the middle (800-1,400 ms) and late time windows(1,400-2,000 ms). Furthermore, depressed individuals exhibited significantly higher LPP amplitudes for sad imagery compared to happy imagery, whereas healthy participants showed the opposite pattern. The present study provides evidence that depressed individuals display abnormal electrophysiological reactivity to sad imagery, which offers a new perspective for understanding the mechanisms underlying depression.
Keywords: Depressed individuals, healthy controls, event-related potentials (ERPs), late positive potential (LPP), and emotional imagery

1.Introduction

Individuals with depression experience more intrusive negative imagery and less vivid positive imagery (Holmes et al., 2016; Weßlau & Steil, 2014). Abnormal emotional imagery may amplify other maladaptive processes in depression, and play an important role in the maintenance and development of depression (Holmes et al. 2009, 2016). Examining imagery biases in depression provides valuable insights into the mechanisms of this disorder (LeMoult & Gotlib, 2019). Moreover, depressed individuals have mood-congruent internal mental representations or schemas (Beck, 1967), and have been supported by numerous studies exploring the neural response of depressed individuals to external emotional stimuli (Benau et al., 2019; Zhou et al., 2021). However, emotional imagery, a mental representations of imagined emotional events or stimuli, might more closely mirror the experiences of individuals with mood disorders (Bauer & MacNamara, 2021). Therefore, exploring the neural correlates of emotional imagery in depressed individuals may contribute to further understand the underlying mechanisms of depression.
The late positive potential (LPP), an event-related potential (ERP) beginning approximately 300-400 ms following stimulus presentation at centroparietal electrodes, is a reliable neural indicator to emotional stimuli(Hajcak & Foti, 2020; Hajcak et al., 2010; Moran et al., 2013). The LPP is sensitive to emotional stimuli and its amplitude elevated degree by emotional material is related to subjective valence or intensity of emotional stimuli (Hajcak et al., 2010). Furthermore, LPP might serve as a neural marker of risk for affective psychopathology (Hajcak & Foti, 2020; Moran et al., 2013), such as depression (Speed et al., 2016). For example, greater pre-treatment LPPs to negative stimuli predicted depression treatment outcome (Stange et al., 2017), and blunted LPP to positive images predicted symptoms of depression (Sandre et al., 2019).
Larger LPP amplitudes to negative stimuli have been reported in adult depression (Benau et al., 2019; Dainer-Best et al., 2017), in adolescents with depression(Auerbach et al., 2015; Burkhouse et al., 2017), in young adulthood with depressive symptoms (Xie et al., 2018), as well as in children with maternal history of depression (Speed et al., 2016). These studies suggested that LPP may be a viable biomarker of negative processing biases in depression. However, there are contradictory results. For example, clinical or non-clinical depressed individuals showed blunted LPP responses to unpleasant images (Nikolin et al., 2022), both pleasant and unpleasant images (Hill et al.,2019), and even all emotional faces (Grunewald et al., 2019). Notably, depressed participants exhibited enhanced LPP for self-referential negative words (Auerbach et al., 2015; Dainer-Best et al., 2017) and negative autobiographical memories(Speed et al., 2020), suggesting that the LPP response to self-related or to internal stimuli may be more stable.
Most previous laboratory studies have employed external stimuli such as negative pictures and words to evoke negative emotion (Benau et al., 2019; Nikolin et al., 2022). However, it is possible that imagined or recalled negative scenarios are more closely to the experience of individuals with mood disorders (Bauer & MacNamara, 2021). Several studies have demonstrated the potential to elicit LPP responses to emotional imagery in both healthy and clinical samples (Bauer & MacNamara, 2021; MacNamara, 2018). For instance, healthy individuals exhibited enhanced LPP responses to emotional imagery relative to neutral imagery (MacNamara, 2018), as well as larger LPP responses to positive imagery versus negative imagery (Marmolejo-Ramos et al., 2015; Suess & Rahman, 2015). The clinical findings indicated that depression was associated with reduced LPP response to negative imagery (Bauer & MacNamara, 2021). However, it should be noted that the depressed participants in this clinical study presented complex comorbid symptoms, including generalized anxiety, social anxiety, and posttraumatic stress disorder. Furthermore, the experimental materials only employed general negative imagery rather than idiographic negative imagery. These studies suggested that the heterogeneity of research methods and participant characteristics may potentially affect the obtained results (Bauer & MacNamara, 2021; Benau et al., 2019; Weinberg et al., 2016). Therefore, there is a need for further investigation into the LPP response to emotional imagery in individuals with depression.
Here, we first screened participants who met the diagnostic criteria for depression, and then used pure emotion images (happy, sad, and neutral scene images) as experimental materials. To examine that emotional imagery can also cause the neural response of depressed individuals like external emotional stimuli, this study examined the LPP responses to emotional imagery. Based on cognitive models of depression (Beck, 1967), we hypothesized that depressed individuals would exhibit an enhanced LPP response to sad imagery than healthy controls. Based on previous studies (Benau et al., 2019; Dainer-Best et al., 2017), we expected that depressed individuals would exhibit an enhanced LPP response to sad imagery relative to happy and neutral imagery, whereas healthy controls would exhibit an enhanced LPP response to happy imagery relative to sad and neutral imagery.

2.Methods

2.1. Participants

Participants were recruited from Jiangxi Normal University through online advertisements. Inclusion criteria for the depressed group were as follows: meeting the diagnostic criteria for current depressive disorder, having a BDI-II score of 14 or higher, and an HDRS-17 score of 8 or higher for depressive symptoms experienced within the past 2 weeks. Participants with bipolar disorder, psychotic disorder, anxiety disorders, or current substance use disorder were excluded. The healthy controls consisted of individuals with no history of neurological or psychiatric illness, a BDI-II score of 13 or lower, and an HDRS-17 score of 7 or lower.
Participants with BDI-II scores above 14 underwent initial screening using Structured Clinical Interview for DSM-5 (SCID; First et al., 2015) during the initial QQ voice interview. Those who met the criteria were invited to the lab for an in-depth clinical interview. All participants were right-handed, had normal or corrected normal vision, provided informed consent prior to the experiment. The Human Research Ethics Committee of Jiangxi Normal University approved the study. EEG data were assessed in 46 depressed participants and 46 healthy controls in the present study. During the encoding-imagery task, 8 participants were excluded due to excessive EEG drift (depression: n=5; control: n=2), or quitting halfway due to discomfort (depression: n=1). Finally, the formal data analysis included 40 depressed participants and 44 healthy controls.

2.2. Measures

First, the current mood disorders were evaluated in all participants with the SCID(First et al., 2015) by two PhDs in clinical psychology supervised by a licensed psychiatrist. Furthermore, the current depression severity and symptomatology were evaluated using the 17-item version of the Hamilton Depression Rating Scale (HDRS-17; Hamilton, 1967) and the Chinese version of the Beck Depression Inventory-Second Edition (BDI-II; Wang et al., 2011). All participants were completed a questionnaire that was contained demographic information and the Vividness of Visual Imagery Questionnaire (VVIQ; Marks, 1973). Demographic characteristics and scale scores of two groups are presented in Table 1. Groups were matched age, education level, and VVIQ score.
Table1. Demographic characteristics and scale scores of depressed individuals and healthy controls